[Issue 12607] Document that IUnknown classes must mark toString with extern(D) when overriding it

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12607

--- Comment #5 from Andrej Mitrovic <andrej.mitrovich at gmail.com> ---
(In reply to Steven Schveighoffer from comment #4)
> Once you go into IUnknown land, there's no coming back out (bwahahaha!)

And somewhat ironically the spec defines IUnknown as using the extern(System)
calling convention, rather than saying it's extern(Windows), as if non-Windows
systems will ever support COM.

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